This invention relates to a food processing appliance and method and, in particular, to a food processing appliance and method especially adapted for the mixing of bread dough.
Food processing appliances generally have the capability of operating in a number of different modes to process a variety of foods with various impellers at impeller speeds appropriate for the specific food being processed. When in a bread processing or dough mixing mode, the temperature of the dough increases with increasing impeller speed. It is desirable to maintain the dough as cool as possible while mixing for proper formation of yeast and gas bubbles. For dough mixing, the impeller has generally been driven at a speed in excess of 1,600 rpm, usually at about 1,780 rpm.
U.S. Pat. No. 4,541,573 discloses a food processor that drives the impeller according to an impeller speed program for mixing dough that includes an initial period of nine seconds of intermittent operation at 1,600 rpm to avoid splattering of dry flour and water ingredients. The initial period is followed by a second period of nine seconds of intermittent operation at 3,300 rpm. Then, the impeller is continuously driven during a third period of 35 seconds at 2,500 rpm. The speed program ends with a final period of 32 seconds of intermittent operation between 1,600 rpm and 2,500 rpm. Except for the initial and final periods, the dough mixing speed is continuously 2,500 rpm.
Gluten is important to making high quality bread without large holes or air cavities. Gluten is either present in the flour or can be added. During the mixing process, gluten is developed to provide a web like consistency to the dough. Mixing with impeller speeds in excess of 1,600 rpm can result in poorly developed gluten, thereby giving rise to poor quality bread.
An impeller used for dough mixing has an S-shape as shown, for example, in the aforementioned U.S. Pat. No. 4,541,573. The S-shaped impeller has two blades that extend from opposed areas along the circumference of an impeller shaft, offset vertically from one another by a small distance. The blades have sharpened leading edges that cut into the dough ball at two distinct levels.
Another impeller used for mixing dough has a planar elongate blade with vertically extending blade tips as shown in U.S. Pat. No. 5,380,086. This blade cuts into the dough ball at only a single level.
Accordingly, there is a need for an improved food processor that is operable at low speeds to mix bread dough, thereby providing a relatively cool dough ball.
A food processor according to the present invention includes a motor that drives an impeller. A mode control establishes a bread dough mixing mode and at least one other mixing mode. A motor control responds to the mode control to operate the motor to drive the impeller at a continuous speed in the range of about 1,400 rpm to about 1,600 rpm during the bread dough mixing mode and at a speed in excess of 1,600 rpm during the other mode. More preferably, the range is about 1,400 rpm to about 1,550 rpm. Most preferably, the continuous speed is about 1,500 rpm. The continuous speed endures for a substantial portion of the dough mixing mode.
The method of the present invention operates a food processor that has a mixing impeller operable in a bread dough mixing mode and at least one other mode. The method signals that the food processor is in the bread dough mixing mode or in the other mode. If in the bread dough mixing mode, the impeller is driven at a continuous speed in the range of about 1,400 rpm to about 1,600 rpm. If in the other mixing mode, the impeller is driven at a speed in excess of 1,600 rpm.
An impeller for mixing dough according to the invention includes an impeller shaft with a blade assembly. The blade assembly includes an upper blade and a lower blade offset vertically from one another and sloping toward one another to thereby slice a relatively wide swath of the dough ball. The upper blade has a downwardly sloping tip and the lower blade has an upwardly sloping tip. The slopes of the upper and lower blades are preferably in the range of about 10xc2x0 to about 30xc2x0. The slopes of the blade tips are preferably less than about 10xc2x0.
The food processor and method of the present invention also incorporates the impeller of the invention to provide high quality dough ball mixing.